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</pre><pre class="rust ">
<span class="comment">// Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT</span>
<span class="comment">// file at the top-level directory of this distribution and at</span>
<span class="comment">// http://rust-lang.org/COPYRIGHT.</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 &lt;LICENSE-APACHE or</span>
<span class="comment">// http://www.apache.org/licenses/LICENSE-2.0&gt; or the MIT license</span>
<span class="comment">// &lt;LICENSE-MIT or http://opensource.org/licenses/MIT&gt;, at your</span>
<span class="comment">// option. This file may not be copied, modified, or distributed</span>
<span class="comment">// except according to those terms.</span>

<span class="comment">// This is the backtracking matching engine. It has the same exact capability</span>
<span class="comment">// as the full NFA simulation, except it is artificially restricted to small</span>
<span class="comment">// regexes on small inputs because of its memory requirements.</span>
<span class="comment">//</span>
<span class="comment">// In particular, this is a *bounded* backtracking engine. It retains worst</span>
<span class="comment">// case linear time by keeping track of the states that is has visited (using a</span>
<span class="comment">// bitmap). Namely, once a state is visited, it is never visited again. Since a</span>
<span class="comment">// state is keyed by `(instruction index, input index)`, we have that its time</span>
<span class="comment">// complexity is `O(mn)` (i.e., linear in the size of the search text).</span>
<span class="comment">//</span>
<span class="comment">// The backtracking engine can beat out the NFA simulation on small</span>
<span class="comment">// regexes/inputs because it doesn&#39;t have to keep track of multiple copies of</span>
<span class="comment">// the capture groups. In benchmarks, the backtracking engine is roughly twice</span>
<span class="comment">// as fast as the full NFA simulation. Note though that its performance doesn&#39;t</span>
<span class="comment">// scale, even if you&#39;re willing to live with the memory requirements. Namely,</span>
<span class="comment">// the bitset has to be zeroed on each execution, which becomes quite expensive</span>
<span class="comment">// on large bitsets.</span>

<span class="kw">use</span> <span class="ident">exec</span>::<span class="ident">ProgramCache</span>;
<span class="kw">use</span> <span class="ident">input</span>::{<span class="ident">Input</span>, <span class="ident">InputAt</span>};
<span class="kw">use</span> <span class="ident">prog</span>::{<span class="ident">Program</span>, <span class="ident">InstPtr</span>};
<span class="kw">use</span> <span class="ident">re_trait</span>::<span class="ident">Slot</span>;

<span class="kw">type</span> <span class="ident">Bits</span> <span class="op">=</span> <span class="ident">u32</span>;

<span class="kw">const</span> <span class="ident">BIT_SIZE</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">32</span>;
<span class="kw">const</span> <span class="ident">MAX_SIZE_BYTES</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">256</span> <span class="op">*</span> (<span class="number">1</span> <span class="op">&lt;&lt;</span> <span class="number">10</span>); <span class="comment">// 256 KB</span>

<span class="doccomment">/// Returns true iff the given regex and input should be executed by this</span>
<span class="doccomment">/// engine with reasonable memory usage.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">should_exec</span>(<span class="ident">num_insts</span>: <span class="ident">usize</span>, <span class="ident">text_len</span>: <span class="ident">usize</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
    <span class="comment">// Total memory usage in bytes is determined by:</span>
    <span class="comment">//</span>
    <span class="comment">//   ((len(insts) * (len(input) + 1) + bits - 1) / bits) * (size_of(u32))</span>
    <span class="comment">//</span>
    <span class="comment">// The actual limit picked is pretty much a heuristic.</span>
    <span class="comment">// See: https://github.com/rust-lang-nursery/regex/issues/215</span>
    <span class="kw">let</span> <span class="ident">size</span> <span class="op">=</span> ((<span class="ident">num_insts</span> <span class="op">*</span> (<span class="ident">text_len</span> <span class="op">+</span> <span class="number">1</span>) <span class="op">+</span> <span class="ident">BIT_SIZE</span> <span class="op">-</span> <span class="number">1</span>) <span class="op">/</span> <span class="ident">BIT_SIZE</span>) <span class="op">*</span> <span class="number">4</span>;
    <span class="ident">size</span> <span class="op">&lt;=</span> <span class="ident">MAX_SIZE_BYTES</span>
}

<span class="doccomment">/// A backtracking matching engine.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Bounded</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="lifetime">&#39;m</span>, <span class="lifetime">&#39;r</span>, <span class="lifetime">&#39;s</span>, <span class="ident">I</span><span class="op">&gt;</span> {
    <span class="ident">prog</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;r</span> <span class="ident">Program</span>,
    <span class="ident">input</span>: <span class="ident">I</span>,
    <span class="ident">matches</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;m</span> <span class="kw-2">mut</span> [<span class="ident">bool</span>],
    <span class="ident">slots</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;s</span> <span class="kw-2">mut</span> [<span class="ident">Slot</span>],
    <span class="ident">m</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="kw-2">mut</span> <span class="ident">Cache</span>,
}

<span class="doccomment">/// Shared cached state between multiple invocations of a backtracking engine</span>
<span class="doccomment">/// in the same thread.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Cache</span> {
    <span class="ident">jobs</span>: <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">Job</span><span class="op">&gt;</span>,
    <span class="ident">visited</span>: <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">Bits</span><span class="op">&gt;</span>,
}

<span class="kw">impl</span> <span class="ident">Cache</span> {
    <span class="doccomment">/// Create new empty cache for the backtracking engine.</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">_prog</span>: <span class="kw-2">&amp;</span><span class="ident">Program</span>) <span class="op">-&gt;</span> <span class="self">Self</span> {
        <span class="ident">Cache</span> { <span class="ident">jobs</span>: <span class="macro">vec</span><span class="macro">!</span>[], <span class="ident">visited</span>: <span class="macro">vec</span><span class="macro">!</span>[] }
    }
}

<span class="doccomment">/// A job is an explicit unit of stack space in the backtracking engine.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The &quot;normal&quot; representation is a single state transition, which corresponds</span>
<span class="doccomment">/// to an NFA state and a character in the input. However, the backtracking</span>
<span class="doccomment">/// engine must keep track of old capture group values. We use the explicit</span>
<span class="doccomment">/// stack to do it.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Copy</span>, <span class="ident">Debug</span>)]</span>
<span class="kw">enum</span> <span class="ident">Job</span> {
    <span class="ident">Inst</span> { <span class="ident">ip</span>: <span class="ident">InstPtr</span>, <span class="ident">at</span>: <span class="ident">InputAt</span> },
    <span class="ident">SaveRestore</span> { <span class="ident">slot</span>: <span class="ident">usize</span>, <span class="ident">old_pos</span>: <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">usize</span><span class="op">&gt;</span> },
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="lifetime">&#39;m</span>, <span class="lifetime">&#39;r</span>, <span class="lifetime">&#39;s</span>, <span class="ident">I</span>: <span class="ident">Input</span><span class="op">&gt;</span> <span class="ident">Bounded</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="lifetime">&#39;m</span>, <span class="lifetime">&#39;r</span>, <span class="lifetime">&#39;s</span>, <span class="ident">I</span><span class="op">&gt;</span> {
    <span class="doccomment">/// Execute the backtracking matching engine.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// If there&#39;s a match, `exec` returns `true` and populates the given</span>
    <span class="doccomment">/// captures accordingly.</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">exec</span>(
        <span class="ident">prog</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;r</span> <span class="ident">Program</span>,
        <span class="ident">cache</span>: <span class="kw-2">&amp;</span><span class="ident">ProgramCache</span>,
        <span class="ident">matches</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;m</span> <span class="kw-2">mut</span> [<span class="ident">bool</span>],
        <span class="ident">slots</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;s</span> <span class="kw-2">mut</span> [<span class="ident">Slot</span>],
        <span class="ident">input</span>: <span class="ident">I</span>,
        <span class="ident">start</span>: <span class="ident">usize</span>,
    ) <span class="op">-&gt;</span> <span class="ident">bool</span> {
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cache</span> <span class="op">=</span> <span class="ident">cache</span>.<span class="ident">borrow_mut</span>();
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cache</span> <span class="op">=</span> <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">cache</span>.<span class="ident">backtrack</span>;
        <span class="kw">let</span> <span class="ident">start</span> <span class="op">=</span> <span class="ident">input</span>.<span class="ident">at</span>(<span class="ident">start</span>);
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">b</span> <span class="op">=</span> <span class="ident">Bounded</span> {
            <span class="ident">prog</span>: <span class="ident">prog</span>,
            <span class="ident">input</span>: <span class="ident">input</span>,
            <span class="ident">matches</span>: <span class="ident">matches</span>,
            <span class="ident">slots</span>: <span class="ident">slots</span>,
            <span class="ident">m</span>: <span class="ident">cache</span>,
        };
        <span class="ident">b</span>.<span class="ident">exec_</span>(<span class="ident">start</span>)
    }

    <span class="doccomment">/// Clears the cache such that the backtracking engine can be executed</span>
    <span class="doccomment">/// on some input of fixed length.</span>
    <span class="kw">fn</span> <span class="ident">clear</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) {
        <span class="comment">// Reset the job memory so that we start fresh.</span>
        <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">jobs</span>.<span class="ident">clear</span>();

        <span class="comment">// Now we need to clear the bit state set.</span>
        <span class="comment">// We do this by figuring out how much space we need to keep track</span>
        <span class="comment">// of the states we&#39;ve visited.</span>
        <span class="comment">// Then we reset all existing allocated space to 0.</span>
        <span class="comment">// Finally, we request more space if we need it.</span>
        <span class="comment">//</span>
        <span class="comment">// This is all a little circuitous, but doing this unsafely</span>
        <span class="comment">// doesn&#39;t seem to have a measurable impact on performance.</span>
        <span class="comment">// (Probably because backtracking is limited to such small</span>
        <span class="comment">// inputs/regexes in the first place.)</span>
        <span class="kw">let</span> <span class="ident">visited_len</span> <span class="op">=</span>
            (<span class="self">self</span>.<span class="ident">prog</span>.<span class="ident">len</span>() <span class="op">*</span> (<span class="self">self</span>.<span class="ident">input</span>.<span class="ident">len</span>() <span class="op">+</span> <span class="number">1</span>) <span class="op">+</span> <span class="ident">BIT_SIZE</span> <span class="op">-</span> <span class="number">1</span>)
            <span class="op">/</span>
            <span class="ident">BIT_SIZE</span>;
        <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">visited</span>.<span class="ident">truncate</span>(<span class="ident">visited_len</span>);
        <span class="kw">for</span> <span class="ident">v</span> <span class="kw">in</span> <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">visited</span> {
            <span class="kw-2">*</span><span class="ident">v</span> <span class="op">=</span> <span class="number">0</span>;
        }
        <span class="kw">if</span> <span class="ident">visited_len</span> <span class="op">&gt;</span> <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">visited</span>.<span class="ident">len</span>() {
            <span class="kw">let</span> <span class="ident">len</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">visited</span>.<span class="ident">len</span>();
            <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">visited</span>.<span class="ident">reserve_exact</span>(<span class="ident">visited_len</span> <span class="op">-</span> <span class="ident">len</span>);
            <span class="kw">for</span> _ <span class="kw">in</span> <span class="number">0</span>..(<span class="ident">visited_len</span> <span class="op">-</span> <span class="ident">len</span>) {
                <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">visited</span>.<span class="ident">push</span>(<span class="number">0</span>);
            }
        }
    }

    <span class="doccomment">/// Start backtracking at the given position in the input, but also look</span>
    <span class="doccomment">/// for literal prefixes.</span>
    <span class="kw">fn</span> <span class="ident">exec_</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="kw-2">mut</span> <span class="ident">at</span>: <span class="ident">InputAt</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
        <span class="self">self</span>.<span class="ident">clear</span>();
        <span class="comment">// If this is an anchored regex at the beginning of the input, then</span>
        <span class="comment">// we&#39;re either already done or we only need to try backtracking once.</span>
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">prog</span>.<span class="ident">is_anchored_start</span> {
            <span class="kw">return</span> <span class="kw">if</span> <span class="op">!</span><span class="ident">at</span>.<span class="ident">is_start</span>() {
                <span class="bool-val">false</span>
            } <span class="kw">else</span> {
                <span class="self">self</span>.<span class="ident">backtrack</span>(<span class="ident">at</span>)
            };
        }
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">matched</span> <span class="op">=</span> <span class="bool-val">false</span>;
        <span class="kw">loop</span> {
            <span class="kw">if</span> <span class="op">!</span><span class="self">self</span>.<span class="ident">prog</span>.<span class="ident">prefixes</span>.<span class="ident">is_empty</span>() {
                <span class="ident">at</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">input</span>.<span class="ident">prefix_at</span>(<span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">prog</span>.<span class="ident">prefixes</span>, <span class="ident">at</span>) {
                    <span class="prelude-val">None</span> <span class="op">=&gt;</span> <span class="kw">break</span>,
                    <span class="prelude-val">Some</span>(<span class="ident">at</span>) <span class="op">=&gt;</span> <span class="ident">at</span>,
                };
            }
            <span class="ident">matched</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">backtrack</span>(<span class="ident">at</span>) <span class="op">||</span> <span class="ident">matched</span>;
            <span class="kw">if</span> <span class="ident">matched</span> <span class="op">&amp;&amp;</span> <span class="self">self</span>.<span class="ident">prog</span>.<span class="ident">matches</span>.<span class="ident">len</span>() <span class="op">==</span> <span class="number">1</span> {
                <span class="kw">return</span> <span class="bool-val">true</span>;
            }
            <span class="kw">if</span> <span class="ident">at</span>.<span class="ident">is_end</span>() {
                <span class="kw">break</span>;
            }
            <span class="ident">at</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">input</span>.<span class="ident">at</span>(<span class="ident">at</span>.<span class="ident">next_pos</span>());
        }
        <span class="ident">matched</span>
    }

    <span class="doccomment">/// The main backtracking loop starting at the given input position.</span>
    <span class="kw">fn</span> <span class="ident">backtrack</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">start</span>: <span class="ident">InputAt</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
        <span class="comment">// N.B. We use an explicit stack to avoid recursion.</span>
        <span class="comment">// To avoid excessive pushing and popping, most transitions are handled</span>
        <span class="comment">// in the `step` helper function, which only pushes to the stack when</span>
        <span class="comment">// there&#39;s a capture or a branch.</span>
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">matched</span> <span class="op">=</span> <span class="bool-val">false</span>;
        <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">jobs</span>.<span class="ident">push</span>(<span class="ident">Job</span>::<span class="ident">Inst</span> { <span class="ident">ip</span>: <span class="number">0</span>, <span class="ident">at</span>: <span class="ident">start</span> });
        <span class="kw">while</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">job</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">jobs</span>.<span class="ident">pop</span>() {
            <span class="kw">match</span> <span class="ident">job</span> {
                <span class="ident">Job</span>::<span class="ident">Inst</span> { <span class="ident">ip</span>, <span class="ident">at</span> } <span class="op">=&gt;</span> {
                    <span class="kw">if</span> <span class="self">self</span>.<span class="ident">step</span>(<span class="ident">ip</span>, <span class="ident">at</span>) {
                        <span class="comment">// Only quit if we&#39;re matching one regex.</span>
                        <span class="comment">// If we&#39;re matching a regex set, then mush on and</span>
                        <span class="comment">// try to find other matches (if we want them).</span>
                        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">prog</span>.<span class="ident">matches</span>.<span class="ident">len</span>() <span class="op">==</span> <span class="number">1</span> {
                            <span class="kw">return</span> <span class="bool-val">true</span>;
                        }
                        <span class="ident">matched</span> <span class="op">=</span> <span class="bool-val">true</span>;
                    }
                }
                <span class="ident">Job</span>::<span class="ident">SaveRestore</span> { <span class="ident">slot</span>, <span class="ident">old_pos</span> } <span class="op">=&gt;</span> {
                    <span class="kw">if</span> <span class="ident">slot</span> <span class="op">&lt;</span> <span class="self">self</span>.<span class="ident">slots</span>.<span class="ident">len</span>() {
                        <span class="self">self</span>.<span class="ident">slots</span>[<span class="ident">slot</span>] <span class="op">=</span> <span class="ident">old_pos</span>;
                    }
                }
            }
        }
        <span class="ident">matched</span>
    }

    <span class="kw">fn</span> <span class="ident">step</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="kw-2">mut</span> <span class="ident">ip</span>: <span class="ident">InstPtr</span>, <span class="kw-2">mut</span> <span class="ident">at</span>: <span class="ident">InputAt</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
        <span class="kw">use</span> <span class="ident">prog</span>::<span class="ident">Inst</span>::<span class="kw-2">*</span>;
        <span class="kw">loop</span> {
            <span class="comment">// This loop is an optimization to avoid constantly pushing/popping</span>
            <span class="comment">// from the stack. Namely, if we&#39;re pushing a job only to run it</span>
            <span class="comment">// next, avoid the push and just mutate `ip` (and possibly `at`)</span>
            <span class="comment">// in place.</span>
            <span class="kw">match</span> <span class="self">self</span>.<span class="ident">prog</span>[<span class="ident">ip</span>] {
                <span class="ident">Match</span>(<span class="ident">slot</span>) <span class="op">=&gt;</span> {
                    <span class="kw">if</span> <span class="ident">slot</span> <span class="op">&lt;</span> <span class="self">self</span>.<span class="ident">matches</span>.<span class="ident">len</span>() {
                        <span class="self">self</span>.<span class="ident">matches</span>[<span class="ident">slot</span>] <span class="op">=</span> <span class="bool-val">true</span>;
                    }
                    <span class="kw">return</span> <span class="bool-val">true</span>;
                }
                <span class="ident">Save</span>(<span class="kw-2">ref</span> <span class="ident">inst</span>) <span class="op">=&gt;</span> {
                    <span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="kw-2">&amp;</span><span class="ident">old_pos</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">slots</span>.<span class="ident">get</span>(<span class="ident">inst</span>.<span class="ident">slot</span>) {
                        <span class="comment">// If this path doesn&#39;t work out, then we save the old</span>
                        <span class="comment">// capture index (if one exists) in an alternate</span>
                        <span class="comment">// job. If the next path fails, then the alternate</span>
                        <span class="comment">// job is popped and the old capture index is restored.</span>
                        <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">jobs</span>.<span class="ident">push</span>(<span class="ident">Job</span>::<span class="ident">SaveRestore</span> {
                            <span class="ident">slot</span>: <span class="ident">inst</span>.<span class="ident">slot</span>,
                            <span class="ident">old_pos</span>: <span class="ident">old_pos</span>,
                        });
                        <span class="self">self</span>.<span class="ident">slots</span>[<span class="ident">inst</span>.<span class="ident">slot</span>] <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">at</span>.<span class="ident">pos</span>());
                    }
                    <span class="ident">ip</span> <span class="op">=</span> <span class="ident">inst</span>.<span class="ident">goto</span>;
                }
                <span class="ident">Split</span>(<span class="kw-2">ref</span> <span class="ident">inst</span>) <span class="op">=&gt;</span> {
                    <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">jobs</span>.<span class="ident">push</span>(<span class="ident">Job</span>::<span class="ident">Inst</span> { <span class="ident">ip</span>: <span class="ident">inst</span>.<span class="ident">goto2</span>, <span class="ident">at</span>: <span class="ident">at</span> });
                    <span class="ident">ip</span> <span class="op">=</span> <span class="ident">inst</span>.<span class="ident">goto1</span>;
                }
                <span class="ident">EmptyLook</span>(<span class="kw-2">ref</span> <span class="ident">inst</span>) <span class="op">=&gt;</span> {
                    <span class="kw">if</span> <span class="self">self</span>.<span class="ident">input</span>.<span class="ident">is_empty_match</span>(<span class="ident">at</span>, <span class="ident">inst</span>) {
                        <span class="ident">ip</span> <span class="op">=</span> <span class="ident">inst</span>.<span class="ident">goto</span>;
                    } <span class="kw">else</span> {
                        <span class="kw">return</span> <span class="bool-val">false</span>;
                    }
                }
                <span class="ident">Char</span>(<span class="kw-2">ref</span> <span class="ident">inst</span>) <span class="op">=&gt;</span> {
                    <span class="kw">if</span> <span class="ident">inst</span>.<span class="ident">c</span> <span class="op">==</span> <span class="ident">at</span>.<span class="ident">char</span>() {
                        <span class="ident">ip</span> <span class="op">=</span> <span class="ident">inst</span>.<span class="ident">goto</span>;
                        <span class="ident">at</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">input</span>.<span class="ident">at</span>(<span class="ident">at</span>.<span class="ident">next_pos</span>());
                    } <span class="kw">else</span> {
                        <span class="kw">return</span> <span class="bool-val">false</span>;
                    }
                }
                <span class="ident">Ranges</span>(<span class="kw-2">ref</span> <span class="ident">inst</span>) <span class="op">=&gt;</span> {
                    <span class="kw">if</span> <span class="ident">inst</span>.<span class="ident">matches</span>(<span class="ident">at</span>.<span class="ident">char</span>()) {
                        <span class="ident">ip</span> <span class="op">=</span> <span class="ident">inst</span>.<span class="ident">goto</span>;
                        <span class="ident">at</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">input</span>.<span class="ident">at</span>(<span class="ident">at</span>.<span class="ident">next_pos</span>());
                    } <span class="kw">else</span> {
                        <span class="kw">return</span> <span class="bool-val">false</span>;
                    }
                }
                <span class="ident">Bytes</span>(<span class="kw-2">ref</span> <span class="ident">inst</span>) <span class="op">=&gt;</span> {
                    <span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">b</span>) <span class="op">=</span> <span class="ident">at</span>.<span class="ident">byte</span>() {
                        <span class="kw">if</span> <span class="ident">inst</span>.<span class="ident">matches</span>(<span class="ident">b</span>) {
                            <span class="ident">ip</span> <span class="op">=</span> <span class="ident">inst</span>.<span class="ident">goto</span>;
                            <span class="ident">at</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">input</span>.<span class="ident">at</span>(<span class="ident">at</span>.<span class="ident">next_pos</span>());
                            <span class="kw">continue</span>;
                        }
                    }
                    <span class="kw">return</span> <span class="bool-val">false</span>;
                }
            }
            <span class="kw">if</span> <span class="self">self</span>.<span class="ident">has_visited</span>(<span class="ident">ip</span>, <span class="ident">at</span>) {
                <span class="kw">return</span> <span class="bool-val">false</span>;
            }
        }
    }

    <span class="kw">fn</span> <span class="ident">has_visited</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">ip</span>: <span class="ident">InstPtr</span>, <span class="ident">at</span>: <span class="ident">InputAt</span>) <span class="op">-&gt;</span> <span class="ident">bool</span> {
        <span class="kw">let</span> <span class="ident">k</span> <span class="op">=</span> <span class="ident">ip</span> <span class="op">*</span> (<span class="self">self</span>.<span class="ident">input</span>.<span class="ident">len</span>() <span class="op">+</span> <span class="number">1</span>) <span class="op">+</span> <span class="ident">at</span>.<span class="ident">pos</span>();
        <span class="kw">let</span> <span class="ident">k1</span> <span class="op">=</span> <span class="ident">k</span> <span class="op">/</span> <span class="ident">BIT_SIZE</span>;
        <span class="kw">let</span> <span class="ident">k2</span> <span class="op">=</span> <span class="ident">usize_to_u32</span>(<span class="number">1</span> <span class="op">&lt;&lt;</span> (<span class="ident">k</span> <span class="op">&amp;</span> (<span class="ident">BIT_SIZE</span> <span class="op">-</span> <span class="number">1</span>)));
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">visited</span>[<span class="ident">k1</span>] <span class="op">&amp;</span> <span class="ident">k2</span> <span class="op">==</span> <span class="number">0</span> {
            <span class="self">self</span>.<span class="ident">m</span>.<span class="ident">visited</span>[<span class="ident">k1</span>] <span class="op">|=</span> <span class="ident">k2</span>;
            <span class="bool-val">false</span>
        } <span class="kw">else</span> {
            <span class="bool-val">true</span>
        }
    }
}

<span class="kw">fn</span> <span class="ident">usize_to_u32</span>(<span class="ident">n</span>: <span class="ident">usize</span>) <span class="op">-&gt;</span> <span class="ident">u32</span> {
    <span class="kw">if</span> (<span class="ident">n</span> <span class="kw">as</span> <span class="ident">u64</span>) <span class="op">&gt;</span> (::<span class="ident">std</span>::<span class="ident">u32</span>::<span class="ident">MAX</span> <span class="kw">as</span> <span class="ident">u64</span>) {
        <span class="macro">panic</span><span class="macro">!</span>(<span class="string">&quot;BUG: {} is too big to fit into u32&quot;</span>, <span class="ident">n</span>)
    }
    <span class="ident">n</span> <span class="kw">as</span> <span class="ident">u32</span>
}
</pre>
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